Molybdenum disulfide has long been known as a desirable additive for use in lubricating oil compositions. Molybdenum disulfide is ordinarily finely ground and then dispersed in the lubricating oil composition to impart friction modifying and antiwear properties. However, one of the major detriments to using finely ground molybdenum disulfide is its lack of solubility.
As an alternative to using finely ground molybdenum disulfide as a friction modifier, a number of other approaches involving various salts of molybdenum compounds have been employed. Molybdenum dithiocarbamates (MoDTC) and molybdenum dithiophosphates (MoDTP) are well known in the art to impart friction modifying properties. Representative compositions of MoDTC are described in Larson et al., U.S. Pat. No. 3,419,589, which teaches molybdenum (VI) dioxide dialkyldithiocarbamates; Farmer et al., U.S. Pat. No. 3,509,051, which teaches sulfurized oxymolybdenum dithiocarbamates; and Sakurai et al., U.S. Pat. No. 4,098,705, which teaches sulfur containing molybdenum dihydrocarbyl dithiocarbamate compositions. Representative compounds of MoDTP are the compositions described in Rowan et al., U.S. Pat. No. 3,494,866, such as oxymolybdenum diisopropylphosphorodithioate.
Another method of incorporating molybdenum compounds in oil is to prepare a colloidal complex of molybdenum disulfide or oxysulfides dispersed using known dispersants. Known dispersants include basic nitrogen containing compounds including succinimides, carboxylic acid amides, phosphonoamides, thiophosphonoamides, Mannich bases, and hydrocarbonpolyamines. King et al., U.S. Pat. No. 4,263,152; King et al., U.S. Pat. No. 4,261,843; and King et al., U.S. Pat. No. 4,259,195 teach molybdenum compounds used as anti-oxidant and anti-wear additives comprising an acidic molybdenum compound and a basic nitrogen compound which acts as a dispersant.
DeVries et al., U.S. Pat. No. 4,259,194 discloses a sulfur containing additive comprising the reaction product of ammonium tetrathiomolybdate and a basic nitrogen compound for use as an anti-oxidant, anti-wear agent, and friction modifier.
Nemo, U.S. Pat. No. 4,705,643 teaches the preparation of carboxylic acid amides as detergent additives in lubricating oils.
Udding et al., U.S. Pat. No. 5,468,891 describes antifriction additives for lubricating oils comprising a molybdenum-containing complex prepared by reacting an alkaline earth metal salt of a carboxylic acid, an amine and a source of cationic molybdenum, wherein the ratio of the number of equivalents of acid groups to the number of moles of molybdenum (eq:mol) is in the range from 1:10 to 10:1, and the ratio of the number of equivalents of acid groups to the number of moles of amine (eq:mol) is in the range from 20:1 to 1:10.
Ruhe, Jr. et al., U.S. Pat. No. 6,962,896 describes antioxidant additives for lubricating oils comprising low color molybdenum compounds and polyamide dispersants including molybdenum oxysulfide polyamides.
Gatto et al., U.S. Pat. No. 6,174,842 discloses a lubricating oil composition comprising a lubricating oil, an oil-soluble molybdenum compound substantially free of reactive sulfur, an oil-soluble diarylamine and a calcium phenate as an anti-wear and anti-oxidant additive.
John et al., U.S. Pat. No. 7,309,680 discloses a process of reacting in a polar medium an oil soluble or oil dispersible thiomolybdate salt with an ammonium sulfide compound.
Many molybdenum technologies that appear in the patent literature deliver high levels of color when used even at moderate levels in crankcase oils. A non-discoloring molybdenum source is important because highly colored oils imply to the end consumer that the oil is “used” and therefore not capable of delivering the maximum amount of protection to the engine. When these highly colored molybdenum sources are used at low levels, e.g. 100-150 ppm delivered molybdenum as is typically required for oxidation, deposit and wear control, discoloration is not substantial but may still be visible. However, when these highly colored molybdenum compounds are used at high levels, e.g. 400-1000 ppm (or higher) delivered molybdenum as is generally required for friction modification, discoloration is often significant. Traditionally, the color of fully formulated crankcase oils has been determined using the ASTM D 6045 color scale. The amount of acceptable finished lubricant darkening depends on the customer and application. While there are no set standards for the amount of discoloration or darkening that is allowed; certain customers may find it difficult to market and sell such dark crankcase oils. Moreover, many of the molybdenum technologies that appear in the patent literature contain sulfur which can further lead to discoloration. Some forms of sulfur can also be detrimental and corrosive to copper, however sulfur incorporation can have beneficial properties such as antiwear functions of serve as friction modifiers when employed in finished lubricants. Accordingly one aspect of the present invention is directed to the preparation of a sulfurized molybdenum complex having improved color and sulfur functionality while treating the complex with compounds to mitigate the active sulfur detriments.